Fish are the best source of omega-3 fatty acids but eating too much fish comes with the risk of ingesting mercury and other toxins. Mercury should be avoided whenever possible. Read on to learn which fish contain high omega-3 levels and low mercury levels.
The Benefit from Eating Fish
Fish is a great source of omega-3 fatty acids. They are polyunsaturated which means that they are liquid at room temperature unlike saturated fats like butter. Polyunsaturated fats are better for your health than saturated fats because they are anti-inflammatory rather than pro-inflammatory. Omega-3 is best known for its potential as an anti-inflammatory properties that may also help to lower the risk of certain chronic conditions, from arthritis to heart issues.1
These fatty acids also have a role in a number of cellular functions such as neuronal cell signaling and of the cell membrane structure and fluidity.1 They may also help to support healthy blood pressures, glucose tolerance, and the nervous system.
The three main omega-3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosohexaenoic acid (DHA). Most of omega-3’s health effects come from EPA and DHA, while ALA must be converted into DHA or EPA in the body before it can be used.
The human body is incapable of producing omega-3 fatty acids on its own, meaning that they can only be introduced via your diet. ALA is more common in plant-based foods, including flax, soybeans, pumpkin seeds, and walnuts. EPA and DHA are found in coldwater fish and other marine sources, including fungi, algae, and sponges.1
Best Fish for Omega-3 Levels
While omega-3 fatty acids can be found in nearly all coldwater fish, the highest amounts of omega-3 can be found in oily fish or fatty fish.2 This includes:
- Salmon
- Herring
- Mackerel
- Anchovies
- Menhaden
- Sardines
However, it’s important to understand that these fish do not produce omega-3 fatty acids on their own. Just like humans, most fish have to get their omega-3 fatty acids via their diet. Marine algae and plankton, which these oily fish feed on, are the main producers of DHA and EPA. Freshwater fish are better at elongating short-chained omega-3 fatty acids into DHA and EPA, but they still get most of their omega-3 from their diet.3
Wild fish have more Omega 3 than farmed fish
This presents a challenge for farmed fish as they do not have access to the omega-3-rich plankton and algae of wild fish. Farmed fish get their omega-3 fatty acids via omega-3 added to their food. In fact, about 80 percent of all fish oil produced is consumed by the fish farming industry. Giving farmed fish wild fish oil to consume helps ensure that farmed fish have similar amounts of omega-3 content as wild fish.3
...But wild fish also have mercury and other heavy metal pollutants.
However, this may be problematic because the wild fish oil added to food for farmed fish may also contain heavy metal pollutants such as mercury, dioxin, and polychlorinated biphenyls (PCBs). While mercury is often the main concern, dioxins and PCBs (a dioxin-like compound) present their own dangers.
Short-term exposure to high dioxin levels may result in altered liver functions and skin lesions. Long-term exposure to dioxin has been associated with impairments to the reproductive system, immune functions, the endocrine system, and developing nervous systems.4
Mercury in Fish Chart
Mercury content can vary from individual fish to fish. Omega-3 containing fish species with mercury content (measured in parts per million) ordered from least to greatest are:
- Menhaden – 0.01 PPM mean5
- Sardine – 0.013 PPM mean
- Anchovies – 0.016 PPM mean
- Fresh/Frozen Salmon – 0.022 PPM mean
- Atlantic Mackerel – 0.05 PPM mean
- Herring – 0.078 PPM mean
- Mackerel Chub (Pacific) – 0.088 PPM mean
- Mackerel Spanish (S. Atlantic) - 0.182 PPM mean
- Mackerel Spanish (Gulf of Mexico) - 0.454 PPM mean
- Mackerel King - 0.73 PPM mean6
Mercury levels increase in larger fish because as larger fish eat smaller fish lower in the food chain, mercury concentrations increase. This means that large, predatory fish found deep in the ocean tend to have the highest levels of mercury. This includes shark, tilefish, swordfish, and king mackerel.10
The Risks of Mercury Consumption
Mercury is a naturally occurring element that is found in rocks and sediment in the earth’s core, including within coal deposits. Mercury can exist in various forms and is best known for staying liquid at room temperature.
Mercury is known to be toxic, particularly in its most common organic form, methylmercury. Although you can be exposed to mercury via certain air emissions or mercury vapors, the most common method of mercury exposure is eating fish and shellfish that contain high levels of methylmercury.7
While high levels of mercury pose dangers to everyone, experts focus recommendations for consumption of food containing mercury for pregnant/breastfeeding women and children. This is because the nervous systems of children are still developing and they are more sensitive to its effects. Children can be exposed to mercury from food and breastmilk. Pregnant mothers can expose their fetuses to mercury via the food they consume.
Mercury exposure is infamous for causing neurological problems. The character “The Mad Hatter” in Alice in Wonderland was mad because he was exposed to mercury through cleaning compounds he used on his top hat.
However, even with these health concerns, eating limited amounts of fatty fish is still recommended by the World Health Organization (WHO). In its study, the WHO concluded that fish in the diets of pregnant women may lower the risk of suboptimal brain development in the child compared to women who did not eat fish. The same report found that maternal exposure to dioxins that stayed under the tolerable monthly intake of 70 pg/kg of body weight resulted in negligible neurodevelopmental risks for the developing fetus.
Consumption of fish was also found to provide a significant source of energy, protein, omega-3 fatty acids, and other important nutrients. Furthermore, among the general adult population, the consumption of oily fish was found to reduce the risk of mortality from coronary heart disease. All of this suggests that the potential benefits of consuming fish and seafood outweigh the potential risk of exposure to mercury and dioxins.9
How to Reduce Your Mercury Consumption
For adult men, experts recommend limiting the consumption of fish with high mercury content to just once per week, though all other fish can be eaten on a regular basis.8 The FDA recommends that adults should feel free to at up to 12 ounces of a variety of cooked seafood per week as long as they avoid larger predatory ocean fish. You should also be aware of any local seafood advisories suggesting increased mercury levels.10
For pregnant women or women who may become pregnant, nursing mothers, and children under the age of 12, experts recommend:
- Eating 8 to 12 ounces per week of a variety of fish and shellfish with a low mercury content. Some of the most common fish low in mercury include catfish, canned light tuna, pollock, salmon, and shrimp.
- Albacore tuna (also referred to as white tuna) contains more mercury than canned light tuna, so try to choose the latter over the former. Limit your albacore consumption to just six ounces per week.
- Consume more alternatives high in Omega 3. For example, take fish oil supplements that have been purified with lower amounts of mercury and toxins.
- Pay attention to local advisories about fish caught in local rivers, lakes, and coastal waters. If there are no advisories provided, you may eat up to six ounces of fish from local waters, but avoid eating any other fish that week. Children under the age of six should limit their consumption of locally caught fish to just one or two ounces per week. Children between the ages of 6 and 12 may eat up to three ounces per week.10
Many people also take fish oil supplements in lieu of eating whole fish. If you are worried about the heavy metal (mercury, dioxin, and PCB) content of the fish oil you’re consuming, you can help to minimize the amount of heavy metals by choosing a fish oil supplement that has been molecularly distilled and purified to remove heavy metals. The distillation and purification process is the reason why certain fish oils contain up to three times more omega-3 oils gram for gram than regular fish oil.
While mercury content in fish may be a concern for some, the potential health benefits and nutritional value of fish may outweigh the risks. Still, if you are concerned about consuming too much mercury in your fish but still want the benefits of omega-3 fatty acids, consider taking a molecularly purified and distilled fish oil supplement instead of consuming fish.
Sources:
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6357022/
- https://ods.od.nih.gov/factsheets/Omega3FattyAcids-HealthProfessional/
- http://www.fao.org/in-action/globefish/fishery-information/resource-detail/en/c/338773/
- https://www.who.int/news-room/fact-sheets/detail/dioxins-and-their-effects-on-human-health
- https://www.ncbi.nlm.nih.gov/pubmed/21292311
- https://www.fda.gov/food/metals/mercury-levels-commercial-fish-and-shellfish-1990-2012
- https://www.epa.gov/mercury/basic-information-about-mercury
- https://www.health.harvard.edu/staying-healthy/is-mercury-in-fish-dangerous
- http://www.fao.org/3/ba0136e/ba0136e00.pdf
- https://www.health.harvard.edu/staying-healthy/what-to-do-about-mercury-in-fish
About the Author:
Dr. Bryan Do, D.O. is an osteopathic physician whose research interests include gastroenterology, immunology, and dermatology. He is particularly interested in the role of probiotics in the gut-brain-skin axis and has written many articles on the topic. He graduated from University of California, Los Angeles (UCLA) before graduating from Marian University College of Osteopathic Medicine in Indianapolis, Indiana and becoming a Doctor of Osteopathic Medicine. Osteopathic physicians are taught to take a holistic approach to medicine and to consider mind, body, and spirit when treating a patient. Osteopathic physicians receive training in Osteopathic Manipulative Medicine (OMM) in addition to the standard rigorous medical school curriculum. Both physicians with a Doctor of Osteopathic Medicine (D.O.) degree as well as a Doctor of Medicine (M.D.) can practice medicine.